The development of advanced nanomaterials is important and challenging for the industrial, biological and medicinal industries. Notably the nanoparticles with or without a solid support are used in a diverse range of fields such as catalysis, sensing, drug delivery, and painting technologies. Several methods are employed for the preparation of nanoparticles and fabrication of nanostructured materials, which can be broadly categorized into a) Bottom-up and b) Top-down technique.
The top-down techniques have been used to obtain bulk quantities of nanoparticles. However, the main problem with this approach is the imperfection of surface structures and significant crystallographic damage with impurities that leads to taking extra care for the design and fabrication of devices. Furthermore, the top-down techniques are limited to the preparation of only a few materials.
On the other hand, the bottom-up techniques provide an excellent control over size, shape and composition of nanoparticles, which can address the industrial needs and nanotechnology in a wide range of applications. This approach includes the wet chemical methods, inert gas phase condensation and pyrolysis. The wet chemical techniques include sol-gel methods, solvo-thermal methods, chemical vapor deposition and others. Here Applicants present the preparation of bulk nanocomposite materials by a new sol-gel and as well as by pyrolysis methods via bottom-up techniques. Using this methodology Applicants prepared a range of new nanocomposite materials (Fe9TiO15, Ti4Pd2O, Sn0.39Ti0.61O2, CoTiO3, Fe9SiO15) and their catalytic applications have been showcased. Further, Applicants' methods represent a possible solution for the preparation and scaling up of novel nanocomposite production on an industrial scale.
The synthetic challenges have limited the production of new types of nanocomposite materials in the industry. Currently, these methodologies, especially the bottom-up techniques face difficulties in producing higher quantities to reach consumer demands. Therefore, the advances in the bottom-up techniques, particularly for the production of bulk quantities of novel nanostructures is important can make a revolution in the present and new scenario of materials and nanotechnology.
A patentability search on the invention disclosed several patents of interest. To be more specific, Brooks et al. (U.S. Pat. No. 7,632,332) discloses methods of producing iron and titanium-containing nanoparticles by reducing iron and titanium-containing precursors with alkali or alkaline-earth metal-containing reducing agents in the presence of a suitable surfactant, and by the thermolysis of iron and titanium-containing precursors without alkali or alkaline-earth metal-containing reducing agents present.
Sun (U.S. Pat. No. 7,128,891) discloses a method and structure for making magnetite nanoparticle materials by mixing an iron salt with alcohol, carboxylic acid and an amine in an organic solvent and heating the mixture to 200-360° C. is described. The size of the particles can be controlled either by changing the iron salt to an acid/amine ratio or by coating small nanoparticles with more iron oxide. Magnetite nanoparticles in the size ranging from 2 nm to 20 nm with a narrow size distribution and can be readily extended to other iron oxide based nanoparticle materials, including M Fe2O4 (M=Co, Ni, Cu, Zn, Cr, Ti, Ba, Mg) nanomaterials, and iron oxide coated nanoparticle materials.
Yun et al. (U.S. Publication No. 20140346408) disclose a method of manufacturing a graphene hybrid material, comprising: preparing nanoparticles, a biomaterial solution, and a graphene oxide solution, mixing the nanoparticles with the biomaterial solution to form biomaterial-coated nanoparticles; mixing the biomaterial-coated nanoparticles with the graphene oxide solution to obtain a graphene oxide/nanoparticle hybrid material; and reducing the graphene oxide/nanoparticle hybrid material to obtain a graphene/nanoparticle hybrid material. The nanoparticles are selected from the group consisting of Au (gold), Ag (silver), Pd (palladium), Pt (platinum), Ni (nickel), Cu (copper), Ru (ruthenium), Rh (rhodamine), TiO2 (titanium dioxide), ZnO (zinc oxide), SnO2 (tin dioxide), MnO2 (manganese dioxide), Co3O4 (cobalt (II, III)), Fe3O4 (magnetite), NiO (nickel(II) oxide), Cu2O (copper (I) oxide), RuO2 (ruthenium dioxide), SiO2 (silicon dioxide), CdS (cadmium sulfide) and CdSe (cadmium selenide) (See Figures and Claims 1, 2).
Pickett (U.S. Pat. No. 7,867,556) disclose a method of producing nanoparticles comprising: effecting conversion of a nanoparticle precursor composition to a material of the nanoparticles, the precursor composition comprising a first precursor species containing a first ion to be incorporated into the nanoparticles and a second precursor species containing a second ion to be incorporated into the nanoparticles, the conversion being effected in the presence of a molecular cluster compound under conditions permitting seeding and growth of the nanoparticles, by dispersing the molecular cluster compound and an initial portion of the nanoparticle precursor composition which is less than the total amount of the nanoparticle precursor composition to be used to produce the nanoparticles in a suitable dispersing medium at a first temperature; increasing a temperature of the dispersing medium containing the cluster compound and precursor composition to a second temperature sufficient to initiate seeding and growth of the nanoparticles on the molecular clusters of the molecular cluster compound; and adding at least one further portion of the nanoparticle precursor composition to the dispersing medium containing the nanoparticles, wherein the temperature of the dispersing medium containing the nanoparticles is increased at least before, during, or after the addition of the at least one further portion of the nanoparticle precursor composition.
General Background
The development of advanced nanomaterials is important and a challenge for the industrial, biological and medicinal applications. Notably the nanoparticles (NPs) with or without a solid support are used in a diverse range of fields such as catalysis, sensing, drug delivery, and painting technology. Several methods are employed for the preparation of NPs and fabrication of nanostructured materials, which can be broadly categorized into a) Bottom-up and b) Top-down techniques. The top-down techniques have been used to obtain bulk quantities of NPs. However, the main problem of this approach is the imperfection of surface structures and significant crystallographic damage with impurities that leads to take extra care and challenge for the design and fabrication of devices. Furthermore, the top-down techniques are limited to the preparation of only few materials.
On the other hand, the bottom-up techniques provide an excellent control over size, shape and composition of nanoparticles, which can address the industrial needs and nanotechnology in a wide range of applications. This approach includes the wet chemical methods, inert gas phase condensation and pyrolysis. The wet chemical techniques include sol-gel methods, solvo-thermal methods, chemical vapor deposition and others. Here we present the preparation of bulk nanocomposite materials by a new sol-gel and as well as by pyrolysis methods via bottom-up techniques. Using this methodology we prepared a range of new nanocomposite materials (Fe9TiO15, Ti4Pd2O, Sn0.39Ti0.61O2, CoTiO3, Fe9SiO15) and their catalytic applications have been showcased. Further, our method represents a possible solution for the preparation and scaling up of novel nanocomposites production on an industrial scale.
Description of a Problem?
The synthetic challenges have limited the production of new types of nanocomposite materials in the industry. Currently, these methodologies, especially the bottom-up techniques face difficulties in producing higher quantities to reach consumer demands. Therefore, the advances in the bottom-up techniques, particularly for the production of bulk quantities of novel nanostructures is important, which can make a revolution in the present and new scenario of materials and nanotechnology.
Current solutions
Among the bottom up techniques, the solvo-thermal and sol-gel methods are preferable for producing large quantities of nanostructured materials. The sol-gel methods are comparatively simple and low-cost; but still require precise control over reaction conditions and pose difficulties to obtain large quantities at industrial scale. Presently, different templates are used for the growth of nanostructures in sol-gel methods. These include the preparation of zeolites, solid layered templates, molecular sieves or polymers. In this method an important step is the formation of a Sol (solid particles in the solution). Use of surfactants and control over pH is required at this stage. Formation of sol is followed by gelation, polycondensation or polyesterification for converting gel into a solid mass entrapping sol in the gel. Drying and calcination at higher temperatures, typically around 1000° C., are used to remove surfactants and organic parts leaving behind metal or metal oxide nanopowders. Chemical reduction methods are also used in presence of reducing agents and emulsions carrying metal ions and supported over a solid template.
Nanomaterials for catalysis applications
Catalysis is a key technology for achieving sustainable processes in chemical, pharmaceutical and material industry. Notably, more than 80% of all chemical products are made via catalysis. For decades, the precious metal-based catalysts modernized organic synthesis from academic labs to industrial production. However, these precious metals are less available, higher in price and exhibit significant toxicity. Therefore for the modern-state-of the-art catalysts, the developments of earth abundant metal-based catalysts continue to be highly important owing to their abundance, lesser price and low toxicity. In recent years number of homogeneous catalysts based on earth abundant metals have been developed for the selective reactions. However, these homogeneous complexes are rather sensitive and/or incorporate sophisticated (synthetically demanding) ligand systems, which are difficult to separate, form the reaction products and are rarely recycled. In contrast, heterogeneous catalysts are extremely stable and can be easily recycled, that are important for the advancement of cost-effective and sustainable industrial processes. Unfortunately, majority of the known heterogeneous catalysts work under drastic conditions and are less selective for the refinement of complex and structurally diverse molecules. In this regard, more progress is required on the development of heterogeneous catalysts. Among heterogeneous materials, the nanocatalysts are of prime importance due to their higher reactivity, selectivity and low energy consumption.
Applicants' solution to the problem
Herein we report a very simple and facile sol-gel method for the synthesis of bi-metal nanostructured materials based on non-noble metals (Fe, Co and Sn) and titanium. Our method involves the synthesis of mixed metal nanoscale composites using low cost precursors, which allows for the synthesis of desired nanocomposite materials with self-scarifying cheaper titanium or silica supports. This procedure does not require any surfactant or any need of pH controlled step. Applicants' method involves the in-situ generation of precursors and their simultaneous entrapment in the gel. This simple one pot synthesis method allows for the synthesis of homogenous size, shape and distribution of targeted nanostructures. Further, this methodology can be applied for the preparation of various nanocomposite materials using different choice of metals and self-scarifying supports. As an example, we prepared Fe, Co and Sn based different nanocomposites with Ti. We also showed the Pd, the noble metal based nanocomposite is also possible. Notably, these materials exhibit excellent catalytic applications for the selective reduction of nitroarenes (Fe—Ti nanocomposite) and for the water splitting (Pd—Ti and Sn—Ti nanocomposite).
Experimental
Synthesis of Nanocomposites
Metal compounds, as precursors of metal composite materials were added in tetrahydrofuran (THF) and polymerization of THF was initiated by addition of a small quantity trifilic acid (TFC) as shown in equation I. No other oxidizing, reducing agent or any surfactant was required. Slow polymerization of THF was allowed out at room temperature. Once gel was formed reaction, mixture was transferred in crucibles and transferred into a furnace. The temperature was raised to 500° C. with a rate of 4° C. per minute and held there for 2 hours.

Where M=Fe, Sn, Co, Pb or any other metal, X=halide, or any organic ligand such as acetylacetonate and pentadienyl. Similarly, Metal-Silicon nanocomposites are prepared.
Proposed Mechanism
TFC used in excess it effects the molecular weight of polymer and synthesis of crown ether oligomers within the reaction matrix. TFC being a non-2ydrolyzable protonic acid can lead to a very high molecular weight poly-THF through a ring opening and chain coupling reaction as shown in the Scheme 1.
The mechanism of polymerization of THF by TFC has been studied expensively over the last 60 years. TFC not only polymerizes THF to a high molecular weight polymer but also yields macrocyclic crown-ether oligomers (predominantly 35-crown-7 cyclic haptamer-shown in Scheme 2) trapped inside poly THF.
It is anticipated that metal ions make complexes with crown ethers, which are trapped inside the polymer matrix and are homogenously distributed with constant stirring. This results in a metallic gel type material as shown in Scheme III. When the resulting metallic gel is decomposed by heating and calcinating at 500° C. for 2 hours, it yields mixed metal composite materials depending upon the precursors used. Supports can directly be added in the THF solution or can be generated in-situ by using their corresponding precursors. We successfully synthesized nanocomposites over titania, silica and alumina.
Catalytic Reduction of Nitroarenes to Anilines:
The oven dried 25 mL ACE pressure tube was charged with magnetic stir bar and 0.5 mmol nitroarene followed by the addition of 2 mL THF. Then, 5-7 mg of Fe-based catalyst and 2.5 mmol of hydrazine hydrate were added sequentially and the pressure tube was flushed with argon. The pressure tube was then closed with screw cap and placed in the preheated aluminium block (100° C.) and the reaction was allowed to progress for 15-18 hr at 100° C. After completion of the reaction, the pressure tube was removed from the aluminium block and cool to room temperature. After cooling down the pressure tube to room temperature, the cap was opened and 100 μL hexadecane as internal standard was added. The catalyst from the reaction mixture was filtered of by the plug of silica and the reaction products were submitted to GC and GC-MS analysis. The products were analysed using GC and GC-MS spectral analysis.
Photoelectrochemical Studies
The photoelectrochemical measurements are carried out by a conventional three electrode system in 1M Na2SO4 (pH=7) as supporting electrolyte. Working electrode was FTO glass coated with 200 μL of 2% nafion suspension of the desired catalyst, Pt gauze served as auxiliary electrode and the standard Ag/AgCl/3M KCl as reference electrode (SCE). All the photoelectrochemical experiments were performed at Metrohm Autolab Potentiostat (PGSTAT302N) instrument. For solar light in laboratory Oriel sol 3A class AAA solar simulator-Newport with following specifications was used; power 100 mW·cm−2 (1 Sun), IEC/JIS/ASTM certified containing 450 Watt Xenon lamp, Air Mass 1.5G Filter, UV cut off filter and 2×2 inch aperture for output beam.
The main features, advantages and benefits of Applicants' solution over the current solutions?
Main Features
Heterometallic nanocomposite materials of desired combinations and structures were synthesized in a straight forward and convenient methodology. The method can be used for the synthesis of bulk quantities unlike chemical vapor deposition or sputtering techniques where the sophisticated instrumentation is required. Furthermore, metal content, composition, size and shape of nanoparticles can be precisely controlled. These materials are characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and electron paramagnetic resonance (EPR).
FIG. 2A displays XRD patterns of nanocomposites synthesized. Pure Fe9TiO15 was prepared when iron and titanium precursors were used in 9:1 ratio. Fe9TiO15 was characterized by, JCPDS File no. 054-1267, with the presence of peaks at 2θ=33.16 (1 0 4), 35.64 (1 1 0), 54.08 (1 1 6), 62.44 (2 1 4) and 64.01 (3 0 0).
Fe9TiO15.TiO2 composite was synthesized using 1:1 ratio of iron and titanium. Calcination of the resultant gel at 500° C. yielded Fe9TiO15.TiO2 composite. Here, TiO2 present as a the self-scarifying support for iron nanoparticles was all in nanostructured anatase phase Which characterized by major peaks at 2θ=25.28° (1 0 1) and 48.05° (2 0 0) (JCPDS File no. 21-1272)), while Fe9TiO15 was characterized by, JCPDS File no. 054-1267, with the presence of peaks at 2θ=33.16 (1 0 4), 35.64 (1 1 0), 54.08 (1 1 6), 62.44 (2 1 4) and 64.01 (3 0 0). All other small peaks also belonged to either Fe9TiO15 or anatase TiO2. The crystallite sizes determined by Debye-Scherrer method for Fe9TiO15 were calculated from XRD spectra and were in the range 11.5-18 nm. TEM images at low resolution showed diameter of most of the particles in between 10-36 nm which infers that nanoparticles consist of 1-2 crystallites. XRD patterns of other nanocomposites are shown in FIG. 2A. Just like Fe9TiO15, other composites also showed XRD in good agreement with the literature and thus synthesis of high crystallinity and purity of nanocomposites.
SEM micrographs show a porous architecture while EDX elemental mapping shows well dispersed Fe and Ti metals present in the vicinity of each other.
HRTEM images show high crystallinity of the particles and anatase-TiO2 particles can be differentiated from Fe9TiO15 nanoparticles by measuring the distance between fringes as shown in FIG. 3. Fe9TiO15 have a distance of 0.236 nm between well-defined fringes while TiO2 particles have 0.33 nm intra-fringes distance.
Advantages and benefits
Inexpensive method
This method is novel, simple and cost-effective for the production of variety of nano-composite materials. Remarkable this protocol can be scaled up to the industrial production of the new nanostructured materials. Further, this method provides an economical and suitable alternative route to the existing expensive methods for the preparation of nano-sized heterostructures.
One pot synthesis
This method is straight forward one pot synthesis and does not require sophisticated instrumentation or specialized chemicals.
Diverse Range of Nanostructures
Further, this method can be applied for the preparation of variety of nanocomposite materials with different choice of metals and self-scarifying supports.
Homogenous Size and Distribution
Nanostructures prepared by this method were homogeneous and spherical in shape. A good agreement was found between particle size determined by TEM and crystallite size determined by Debye-Schererr method from XRD results.
Highly Reproducible Synthesis
This method is reproducible and the materials produced are highly stable.
Possible Uses for the Invention
This method allows for the synthesis of nanocomposites of desired combination and materials which are not synthesized before in their nano-form. This could be a breakthrough for different applications in nanotechnology including but not limited to catalysis, water splitting, fuel cells, super capacitors charge storage and sensing applications.
As an example, here we disclose the two catalytic applications of these materials.
Catalytic Reduction of Nitroarenes to Amines
Anilines constitute central intermediates and key precursors for the synthesis of life science molecules, dyes, materials and petrochemical derivatives. Generally, anilines have been prepared by the reduction of nitroarenes. Despite number of catalysts have been developed for this reaction, still the development of novel and selective catalysts are desired. Here our iron based nanocomposite materials exhibit remarkably activity for highly selective reduction of nitroarenes using hydrazine hydrate reducing agent, which produces water as only byproduct (FIG. 7). The catalyst shows excellent selectivity for the reduction of nitro group in the presence of other reducible moieties (nitrile, amide, ester, halides), in heterocyclic compounds and in structurally diverse molecules. Further, the nitro phenol has been selectively reduced to aminophenol in 88% yield. The presence of nitro-substituted phenols poses a major threat to vital human organs including kidneys, liver and central nervous system. Such nitro-phenols (NP) are soluble in aqueous media and are not naturally degradable. In this regard, the present method offers suitable solution for the conversion of hazardous nitro phenol containing molecules to amino phenols.
Water Splitting
Production of H2 fuel by water splitting using sunlight at a semiconductor/water interface is an efficient green alternative of ever depleting fossil fuels. A lot of research efforts over the years have been devoted to find active semiconducting materials for H2 production. Typically, a photoelectrochemical cell (PEC) is comprised of a p-type or n-type semiconducting material, which generate holes or electrons, respectively, at the semiconductor/water interface. In case of a p-type H+ is reduced to H2 after absorption of sunlight at the semiconducting electrode surface. The quest for low cost, stable and scaleable materials for PEC is highly desired for the present and future energy related issues. Herein, we developed a nanocomposite Ti14Pd2O material, which showed excellent catalytic activity for H2 production in presence of sunlight. The initial results are represented in FIG. 8a. 
Similarly, we prepared another n-type nanocomposites Sn0.39Ti0.61O2, Fe9TiO15, and CoTiO3, which act as excellent water splitting material in PEC cell and preliminary results are shown in FIG. 8 (b-d). To the best of our knowledge all these nanocomposite materials have not been reported for the photochemical water splitting.